Calculation of radiative properties of SF6-C2F4 thermal plasmas-application to radiative transfer in high-voltage circuit breakers modelling

Radiative transfer is a key point for accurate simulations of arcs in high voltage circuit breakers where the plasma is mainly composed, at high current, of a mixture of SF6 and PTFE vapours (C2F4 and decomposition products). Assuming local thermodynamic equilibrium, we have built a database of absorption coefficients over almost 300 000 spectral points, for a pressure range between 1 and 100 bar, temperatures from 300 to 50 000 K, and proportions from pure SF6 to pure C2F4. From these data, we have calculated the mean absorption coefficients (MAC) by considering several definitions of the mean coefficient and several spectral ranges or intervals. The choice between the various definitions was operated using a one dimensional radiative transfer model with imposed temperature profiles. The results showed that a combination of a normal average over the molecular continuum at low temperature, with a mixed definition of Planck average at high temperature gives the most accurate results. The optimization of the number of intervals for the definition of the MAC database was performed and showed that the accuracy on the radiative flux and on the divergence of the flux depends on the temperature profile. A good compromise is obtained with five or seven intervals.